Package and method for attaching an integrated heat spreader

ABSTRACT

In some embodiments, an integrated circuit package includes a substrate and a heat spreader coupled to the substrate by fasteners. Thermal interface material thermally couples the die to the heat spreader. The heat spreader is provided over the die and is attached to the substrate with fasteners rather than a sealant-adhesive. Some examples of suitable fasteners may include rivets, barbed connectors, and gripping clips.

TECHNICAL FIELD

[0001] Embodiments of the present invention pertain to integratedcircuit package manufacturing, and in some embodiments, to techniques toretain heat spreader lids over a die on a substrate.

BACKGROUND

[0002] Manufacture of integrated circuit packages may involve, amongother things, the installation of heat spreaders onto the package.During an installation process, a heat spreader lid may be adhered to asubstrate while the package is mounted in a process carrier. The lid isconventionally affixed to the substrate using an adhesive or a sealant.A thermal interface material may be applied between the die and the heatspreader. Thermal conductivity between the heat spreader and the die maybe dependent on the application force on the lid during curing of thethermal interface material. A clip is typically used to secure thepackage in the process carrier and apply force to the heat spreaderwhile the sealant-adhesive and interface material are cured. To ensureproper heat transfer from the substrate to the heat spreader, the forceasserted by the clip should be maintained within an appropriate range.The use of clips and sealant-adhesive to adhere the heat spreader to thesubstrate presents many manufacturing and process challenges.

[0003] One challenge is that the sealant-adhesive used to secure theheat spreader to the substrate may require additional curing steps inaddition to the curing of the thermal interface material. Anotherproblem is that the sealant-adhesive sometimes delaminates the surfaceof the substrate, especially in highly stressed packages. Anotherproblem is that the insertion and removal of clips requires additionalhandling and assembly steps increasing cost and reducing repeatability.Another problem is that the clips may change their spring/retentionforce over time and temperature affecting the thermal interface betweenthe die and the heat spreader.

[0004] Thus, what is needed is a package and method to attach a heatspreader to a substrate. What is also needed is a package and method toattach a heat spreader to a substrate that reduces the number ofassembly/process steps. What is also needed are a package and method toattach a heat spreader to a substrate that reduces the risk ofdelamination of the substrate surface. What is also needed is a packageand method to attach a heat spreader to a substrate that does notrequire the use of clips.

BRIEF DESCRIPTION OF THE DRAWINGS

[0005] The appended claims are directed to some of the variousembodiments of the present invention. However, the detailed descriptionpresents a more complete understanding of embodiments of the presentinvention when considered in connection with the figures, wherein likereference numbers refer to similar items throughout the figures and:

[0006]FIG. 1 is a cross-sectional view of a portion of a conventionalpackage;

[0007]FIG. 2 is a cross-sectional view of a portion of a package withrivets securing a heat spreader in accordance with some embodiments ofthe present invention;

[0008]FIG. 3 is a cross-sectional view of a portion of a package withrivets securing a heat spreader in accordance with some embodiments ofthe present invention;

[0009]FIG. 4 is a cross-sectional view of a portion of a package withrivets securing a heat spreader in accordance with some embodiments ofthe present invention;

[0010]FIG. 5 is a cross-sectional view of a package withexternal-gripping clips securing a heat spreader in accordance with someembodiments of the present invention;

[0011]FIG. 6 is a cross-sectional view of a package with barbedconnectors securing a heat spreader in accordance with some embodimentsof the present invention;

[0012]FIG. 7 is a cross-sectional view of a package with barbedconnectors securing a heat spreader in accordance with some embodimentsof the present invention;

[0013]FIG. 8 is a perspective view of a portion of a package inaccordance with some embodiments of the present invention; and

[0014]FIG. 9 is a system in accordance with some embodiments of thepresent invention.

DETAILED DESCRIPTION

[0015] The following description and the drawings illustrate specificembodiments of the invention sufficiently to enable those skilled in theart to practice them. Some embodiments may incorporate structural,logical, electrical, process, and other changes. Examples merely typifypossible variations. Individual components and functions are optionalunless explicitly required, and the sequence of operations may vary.Portions and features of some embodiments may be included in orsubstituted for those of others. The scope of embodiments of theinvention encompasses the full ambit of the claims and all availableequivalents of those claims.

[0016] Embodiments or the invention provide an improved package andmethod to attach a heat spreader to a substrate. In some embodiments, anintegrated circuit package and method to attach a heat spreader to asubstrate may reduce the number of assembly/process steps. In someembodiments, a package and method to attach a heat spreader to asubstrate may reduce the risk of delamination of the substrate surface.Embodiments of the invention provide a package and method to attach aheat spreader to a substrate that may eliminate the use of clips.

[0017]FIG. 1 is a cross-sectional view of a conventional package.Conventional package 100 includes substrate 102, die 104 mounted onsubstrate 102, and heat spreader 106. Heat spreader 106 may be thermallycoupled with die 104 with thermal interface material (TIM) 108. Heatspreader 106 may be adhered to substrate 102 with sealant-adhesive 110.TIM 108 and sealant-adhesive 110 are generally cured at an elevatedtemperature. A clamping device, such as a clip or bridge clip, may beused to secure heat spreader 106 on package 100 in a carrier (notillustrated) during curing. The clip helps prevent movement of the heatspreader which may result from expansion of TIM 108 during curing, aswell as movement resulting from other factors.

[0018] One problem with conventional package 100 and associatedpackage-assembly techniques is that sealant-adhesive 110 may requireadditional curing steps beyond the curing of TIM 108. Another problemwith this package configuration and package-assembly technique is thatsealant-adhesive 110 sometimes delaminates the surface of substrate 102,especially in highly stressed packages. Another problem with thispackage configuration and package-assembly technique is that theinsertion and removal of clips requires additional handling and assemblysteps. Another problem with this package configuration andpackage-assembly technique is that the clips may change theirspring/retention force over time and temperature. Another problem isthat the position of the heat spreader may vary.

[0019]FIG. 2 is a cross-sectional view of a portion of a package withrivets securing a heat spreader in accordance with some embodiments ofthe present invention. Package 200 includes substrate 202, die 204mounted on substrate 202, and heat spreader 206 thermally coupled to die204 by TIM 208. TIM 208 may be solder or a polymer material. Inaccordance with the illustrated embodiments, a plurality of fasteners210 couple heat spreader 206 to substrate 202. Although fasteners 210are illustrated as rivets, many other types of fasteners may be used.Examples of suitable fasteners may include rivets, external grippingclips, barbed fasteners, threaded fasteners and non-threaded fasteners.Examples of suitable rivets may include, for example, push broach orpull broach rivets, solid rivets, tubular rivets, compression rivets,bifurcated rivets and metal piercing rivets. Examples of suitablenon-threaded fasteners may include, for example, keys, splines,serrations, press-fit pins and retaining rings. In some embodiments,fasteners 210 may be referred to as micro-fasteners. Fasteners may becomprised of many suitable materials including metals and plastics.Examples of some suitable materials may include nickel alloys, aluminumalloys, brass alloys, carbon and alloy steels, copper alloys, nylon,stainless steel, bronze, and titanium.

[0020] When fasteners 210 comprise rivets, mandrill 212 is pulledthrough the rivet during assembly to expand the end of the rivet belowsubstrate 202. Mandrill 212 and rivet tool portion 218 are removedleaving the rivet. In some embodiments, head 214 of the rivet may belocated in recess 216 of heat spreader 206 so that the surface of theheat spreader opposite the die is planar allowing, for example, a heatsink to be attached thereto.

[0021] In some embodiments in which fasteners 210 comprise rivets, therivets may be almost any commercially available rivet. The rivets maycomprise a pull-broach type of rivet. In some embodiments, the rivetsmay have a diameter ranging from 40 thousandths of an inch to 80thousandths of an inch; however the dimensions of rivets may depend onvarious factors including the size the elements of package 200. Suitablerivets may be purchased, for example, from Textron, Inc.

[0022] Fasteners 210 may be placed around a perimeter of heat spreader206, and in some embodiments, are placed at least at the corners of heatspreader 206. When viewed from above, heat spreader 206 may berectangular and at least four fasteners at the corners may be used. Inthe specific embodiments illustrated in FIG. 2, fasteners 210 may extendcompletely through substrate 202.

[0023] Heat spreader 206 has central region 220 and perimeter region222. Perimeter region 222 may have a thickness greater than centralregion 220 by approximately a height of the die and a thickness of thethermal interface material. The thinner central region and thickerperimeter region allow heat spreader 206 to contact substrate 202 in theperimeter region while leaving space for die 104 and TIM 108 in thecentral region. In this embodiment, the fasteners are received throughholes in the perimeter region and may extend through aligned holes insubstrate 202.

[0024] An assembly process for package 200 may include drilling holesfor fasteners 210 in substrate 202 and heat spreader 206, althoughsubstrate 202 and/or heat spreader 206 may be provided with pre-drilledor pre-fabricated holes. Die 204 may be mounted on substrate 202 eitherbefore or after the holes are made in substrate 202. The assemblyprocess may also include dispensing TIM 208, including any flux, ontodie 204, and placing heat spreader 206 over the die aligning thefastener holes. Fasteners 210 may be inserted through the holes and, inthe case of rivets, “riveting” substrate 202 to heat spreader 206. TIM208 may be cured or re-flowed, as appropriate, for example, at anelevated temperature. In some embodiments, the holes for the fastenersmay be fabricated or formed through laser ablation, stamping orpunching, or by waterjet.

[0025] Package 200 may eliminate sealant-adhesive 110 (FIG. 1) used inconventional packages, along with process steps required to cure thesealant-adhesive. In addition, clips conventionally used during curingmay also be eliminated to significantly reduce the number of packageassembly steps. Furthermore, yield may be improved by the elimination of“sealant stringers” and heat spreader placement variations. The use offasteners 210 may also provide a more rigid package which may improvereliability because tensile stress from the TIM may be reduced. Package200 may also reduce heat spreader tilt.

[0026] In some embodiments, package 200 may be part of a systemcomprising package 200 mounted on a circuit board. The circuit board maybe comprised of an organic or inorganic material. The circuit board maybe a laminate and example organic materials for the circuit board mayinclude BT, FR4, or FR5 for the core material. Examples of suitableinorganic materials for the circuit board include ceramics. In someembodiments, package 200 may be attached to the circuit board withsolder balls, with a PGA socket, with a LGA socket, as well as withother techniques. Die 204 may comprise almost any semiconductor dieincluding, for example, digital signal processors (DSPs),microprocessors, analog integrated circuits, chipsets and memorydevices.

[0027]FIG. 3 is a cross-sectional view of a portion of a package withrivets securing a heat spreader in accordance with some embodiments ofthe present invention. Package 300 may be similar to package 200 (FIG.2), however package 300 may include standoffs 301 between heat spreader306 and substrate 302. Standoffs 301 may be about at least as high as aheight of die 304 and a thickness of TIM 308. In some embodiments,perimeter region 322 of heat spreader 306 may have a thickness less thana thickness of central region 320. Fasteners 310 may be received throughholes in perimeter region 322 of heat spreader 306 which are alignedwith holes in standoffs 301. In the embodiments illustrated in FIG. 3,fasteners 310 do not need to extend completely through substrate 302. Insome embodiments, standoffs 301 may be adhered to the substrate withadhesive 303. In some embodiments, standoffs 301 may be fabricated aspart of the substrate. Standoffs 301 may include either a counter-boredhole or cavity 324 between a surface of the substrate to receive orretain an end of fastener 310. Although package 300 is illustrated withfasteners 310 comprising rivets, fasteners 310 may comprise other typesof fasteners, such as the other types of fasteners listed for fasteners210 (FIG. 2).

[0028] The assembly process for package 300 may be similar to theassembly process for package 200 (FIG. 2), however it may includereceiving the substrate with standoffs 301 included. Alternatively, theassembly process may include adhering standoffs 301 to the substrate302. One advantage to package 300 is that because fasteners 310 do notextend through substrate 302, pins 326 may be provided in a region underfasteners 310.

[0029]FIG. 4 is a cross-sectional view of a portion of a package withrivets securing a heat spreader in accordance with some embodiments ofthe present invention. Package 400 may be similar to package 300 (FIG.3); however heat spreader 406 may have a more uniform thickness inperimeter region 422 and central region 420. Furthermore, standoffs 401may have a height approximately equal to a height of die 404 and TIM408. In this embodiment, fasteners 410 may be push-broach rivets havingheads 414 located in counter-bored holes or recesses 424. Duringassembly, mandrill 412 may be pushed (rather than pulled) to expand aportion of fastener 410 in recess 416 of heat spreader 406. As part ofthe assembly process, fasteners 410 may be positioned prior to adheringstandoffs 401 to substrate 402. One advantage to package 400 is thatheat spreader 406 may be substantially flat which may help reduce costs.Another advantage to package 400 is that pins 426 (e.g., I/O pins orpower/ground pins) may be provided in the region below rivets 410.Although package 400 is illustrated with fasteners 410 comprisingrivets, fasteners 410 may comprise other types of fasteners, such as theother types of fasteners listed for fasteners 210 (FIG. 2).

[0030]FIG. 5 is a cross-sectional view of a package withexternal-gripping clips securing a heat spreader in accordance with someembodiments of the present invention. Package 500 may be similar topackage 400 (FIG. 4) in which heat spreader 506 is substantially planaron the die side. Package 500 includes fasteners 510 which compriseexternal-gripping clips or Timmerman nuts. Head portion 514 of fastener510 may be adhered to a surface of substrate 502 with an adhesive orwith solder. Pin portion 512 of fastener 510 may extend through a holein heat spreader 506. Clip portion 518 may grip pin portion 512 to holdheat spreader 506 in position. Clip portion 518 may be comprised ofmaterials such as plastic or sprung steel. Spacers (not illustrated forclarity) may be included between heat spreader 506 and substrate 502,and in some embodiments, may be similar to standoffs 401 (FIG. 4). Thespacers may be washers provided around fasteners 510. Although package500 is illustrated with fasteners 510 comprising external-grippingclips, fasteners 510 may comprise other types of fasteners, such as theother types of fasteners listed for fasteners 210 (FIG. 2). In addition,fasteners 510 may include threaded fasteners having their heads adheredto substrate 502, with a nut in place of clip portion 518. Heat spreader506 may include recesses 516 allowing clip portion 518 and pin portion512 to remain below the surface of the heat spreader.

[0031] In some embodiments (not illustrated), head portion 514 maybeembedded within substrate 502. In some embodiments (not illustrated),fastener 510 may be inserted through a hole in substrate 502 from thepin side of substrate 502 and head portion 514 may remain below thesubstrate.

[0032] The assembly process for package 500 may include adhering headportion 512 of fasteners 510 to substrate 502, and placing heat spreader506 over the die so that pin portions 512 protrude through correspondingaligned holes in the heat spreader. Clip portion 518 may be pressed overthe pin portion 512 to hold heat spreader 506 in position.

[0033]FIG. 6 is a cross-sectional view of a package with barbedconnectors securing a heat spreader in accordance with some embodimentsof the present invention. Package 600 is similar to package 500 (FIG.5); however fasteners 610 may comprise barbed connectors. Fasteners 610may be embedded in the die side of heat spreader 606 into region 616.Region 616 may be a pre-drilled hole to receive a head of the fastener.Alternatively, fasteners may extend through the heat spreader from theside opposite the die side. In some embodiments, heads of fasteners 610may be adhered to the die side of heat spreader 606.

[0034] Package 600 may also include receivers 612 to receive fasteners610 and prevent fasteners 610 from being pulled out. Once the ends offasteners 610 are inserted into receivers 612, barbs, for example, mayprevent the fasteners from being removed. Receivers 612 may beself-gripping retaining rings or blind cages, and may be comprised of ametal insert which may be included within standoff 601. Standoffs 601may include stiffeners as well as spacers. In some embodimentsillustrated in FIG. 6B, receivers 612 may be located at the surface ofsubstrate 602 and fastener 610 may protrude at least partially into thesubstrate. In some embodiments, illustrated in FIG. 6C, receivers 612may be provided to prevent fastener 610 from protruding into thesubstrate. Receivers may, for example, be comprised of plastic, steel orsprung steel. Fasteners 610 may be a metal or a plastic. Althoughpackage 600 is illustrated with fasteners 610 comprising barbedconnectors, fasteners 610 may comprise other types of fasteners, such asthe other types of fasteners listed for fasteners 210 (FIG. 2).

[0035] For package 600, when a substantially flat heat spreader 606 isused, standoff 601 may be about as high as the height of the die plusthe thickness of the thermal interface material; however other heightstandoffs 601 may also be used, depending on the heat spreader shape.For example, heat spreaders having thinner perimeter regions, such asheat spreader 306 (FIG. 3) may be used, allowing for taller or thickerstandoffs. Heat spreaders having thicker perimeter regions may also beused, such as heat spreader 206 (FIG. 2), allowing for use of shorter orthinner standoffs, or even eliminating the spacers or standoffs.

[0036] The assembly process for package 600 may include snapping heatspreader 606 into position. Fasteners may be inserted into holes ofstandoffs 601 and may snap into receivers 612. The heat spreader may beprovided with fasteners 610 already located in regions 616, or thefasteners may be inserted into regions 616. The thermal interfacematerial between the die and heat spreader may be cured once the heatspreader is snapped into position. Advantages to package 600 and theassociated assembly process are that no curing of sealant-adhesive isrequired to adhere the heat spreader to the surface. No clips arerequired, and the position of the heat spreader doesn't change withcuring. Furthermore, snapping the heat spreader in position eliminatesseveral assembly steps and processes which may help reduce costs.

[0037]FIG. 7 is a cross-sectional view of a package with barbedconnectors securing a heat spreader in accordance with some embodimentsof the present invention. Package 700 is similar to package 600 (FIG. 6)however fasteners 710 may be inserted through heat spreader 706 from theside opposite the die side. Fasteners may be received by receivers 716,which may be similar to receivers 616 (FIG. 6). Fasteners 710 may alsoprotrude at least partially into substrate 702 depending on theirlength, and the thickness or height of standoff 701. Heat spreader 706may be thicker in a perimeter region, such as heat spreader 206 (FIG.2), reducing or eliminating the need for standoffs 701. Alternatively,standoffs 701 may be an integral part of substrate 702, or may beadhered to substrate 702.

[0038] The assembly process for package 700 may include placing heatspreader 706 in position over the die, and inserting fasteners 710 intoaligned holes of the heat spreader and substrate until the fasteners areretained sufficiently in receivers 716. In some embodiments, the surfaceof heat spreader may be provided so that heads 714 of fasteners 710remain at or below the surface opposite the die to allow coupling with aheat sink, for example.

[0039]FIG. 8 is a perspective view of a portion of a package inaccordance with some embodiments of the present invention. Packageportion 800 is illustrated without a heat spreader and includes die 804mounted on substrate 802. Package portion 800 may be suitable for usewith any of the previously discussed packages, although other packageportions are also suitable. Package portion 800 includes one or morestandoffs 801 which may have a height approximately equal to the heightof die 804 plus a thickness of a thermal interface material used. Inthis embodiment, a heat spreader of more uniform thickness may be usedin which the perimeter region has about the same thickness as thecentral region.

[0040] Although standoffs 801 are illustrated as a single elementpositioned around the perimeter of die 804, standoffs 801 may becomprised of separate elements, and may be part of substrate 802, or maybe separate. Holes 803 for the fasteners may be provided at the cornersof the standoff, however additional holes may be provided in otherlocations.

[0041]FIG. 9 is a system in accordance with some embodiments of thepresent invention. System 900 includes package 902 mounted to circuitboard 904. System 900 may be part almost any electronic device includinga computing or processing system or wireless communication device.Package 902 may be one of the package embodiments discussed previously,including package 200 (FIG. 2), package 300 (FIG. 3), package 400 (FIG.4), package 500 (FIG. 5), package 600 (FIG. 6A), or package 700 (FIG.7). Circuit board 904 may be comprised of an organic or inorganicmaterial, or may have a ceramic, organic or metallic core, and may haveone or more of packages 902 coupled thereto and connected electrically.

[0042] Thus, improved packages and methods to attach a heat spreader toa substrate have been described. Also, packages and methods to attach aheat spreader to a substrate that reduces the number of assembly/processsteps have been described. Also, packages and methods to attach a heatspreader to a substrate that reduces the risk of delamination of thesubstrate surface have been described. Also, packages and methods toattach a heat spreader to a substrate that does not require the use ofclips have been described. In some embodiments, the heat spreader isprovided over the die and is attached to the substrate with fastenersrather than a sealant-adhesive. Some examples of suitable fasteners mayinclude rivets, barbed connectors, and gripping clips. The use ofcertain fasteners may allow the heat spreader to be snapped in positionreducing assembly steps and improving positioning alignment. The use offasteners may also help maintain the position of the heat spreader overthe die during curing of the thermal interface material improving thereliability of the interface. Furthermore, the need for curing thesealant-adhesive is eliminated along with the use of clips to hold theheat spreader in position during curing.

[0043] It is emphasized that the Abstract is provided to comply with 37C.F.R. Section 1.72(b) requiring an abstract that will allow the readerto ascertain the nature and gist of the technical disclosure. It issubmitted with the understanding that it will not be used to limit orinterpret the scope or meaning of the claims.

[0044] In the foregoing detailed description, various features areoccasionally grouped together in a single embodiment for the purpose ofstreamlining the disclosure. This method of disclosure is not to beinterpreted as reflecting an intention that the claimed embodiments ofthe subject matter require more features that are expressly recited ineach claim. Rather, as the following claims reflect, inventive subjectmatter lies in less than all features of a single disclosed embodiment.Thus the following claims are hereby incorporated into the detaileddescription, with each claim standing on its own as a separate preferredembodiment.

What is claimed is:
 1. A package comprising: a substrate; a heatspreader coupled to the substrate with a plurality of fasteners; and adie mounted on the substrate and thermally coupled to the heat spreaderwith an interface material.
 2. The package of claim 1 wherein the heatspreader has recesses on a surface opposite the substrate to receiveheads of the fasteners.
 3. The package of claim 2 wherein the fastenersare rivets and wherein the substrate has holes therethrough aligned withholes in a perimeter region of the heat spreader, the rivets to extendthrough the aligned holes in the substrate and the perimeter region. 4.The package of claim 1 wherein the die is coupled to a central region ofthe heat spreader with thermal interface material, wherein the fastenerscouple a perimeter region of the heat spreader region to the substrate.5. The package of claim 4 wherein the perimeter region has a thicknessgreater than the central region by approximately a height of the dieplus a thickness of the thermal interface material, the fastenersprovided through holes in the perimeter region.
 6. The package of claim4 wherein the perimeter region has a thickness less than orapproximately equal to a thickness of the central region, and whereinthe substrate has standoffs to align with portions of the perimeterregion, the standoffs having a height approximately at least as great asa height of the die plus a thickness of the thermal interface material,the fasteners to be received through holes in the perimeter regionaligned with holes in the standoffs.
 7. The package of claim 4 furthercomprising standoffs to align with portions of the perimeter region, thestandoffs having a height approximately at least as great as a height ofthe die plus a thickness of the thermal interface material, thestandoffs adhered to the substrate with an adhesive.
 8. The package ofclaim 4 wherein the substrate includes standoffs to align with portionsof the perimeter region, the standoffs having a height approximately atleast as great as a height of the die plus a thickness of the thermalinterface material, the standoffs being part of the substrate.
 9. Thepackage of claim 6 wherein the standoffs provide at least a partialcavity between a surface of the substrate to receive an end of thefasteners, the fasteners extending through the holes in the heatspreader into the at least partial cavities of the standoffs, thefasteners having a length not exceeding a height approximately at leastas great as a height of the die plus a thickness of the thermalinterface material plus a thickness of the heat spreader in theperimeter region so as not to extend through the surface of thesubstrate.
 10. The package of claim 4 wherein the heat spreader has asubstantially uniform thickness throughout the central region and theperimeter region, and wherein the package further comprises one or morespacers between the substrate and heat spreader in the perimeter region,the one or more spacers having a height approximately equal to a heightof the die and a thickness of the thermal interface material, thefasteners to be received through holes in the perimeter region alignedwith holes in the spacers and holes in the substrate.
 11. The package ofclaim 6 wherein the fasteners comprise push-broach rivets, the standoffsto retain a head of the rivets.
 12. The package of claim 6 wherein thefasteners comprise pull broach rivets.
 13. The package of claim 6wherein the fasteners comprise barbed fasteners, the barbed fasteners tobe received by either retaining rings or blind-cage retaining elementscoupled to the substrate.
 14. The package of claim 13 wherein the barbedfasteners allow the heat spreader to be snapped into position over thedie.
 15. The package of claim 6 wherein the fasteners comprise externalgripping clips, the gripping clips being soldered to a surface of thesubstrate.
 16. The package of claim 6 wherein the fasteners compriseexternal gripping clips, the gripping clips extending through thesubstrate.
 17. The package of claim 1 wherein the fasteners comprisethreaded fasteners.
 18. The package of claim 1 wherein the substrate hasone of either an organic core, or a metallic core, or is a ceramicsubstrate.
 19. A method comprising: positioning a heat spreader over adie region of a substrate; aligning holes in a perimeter region of theheat spreader with holes in the substrate; and fastening the heatspreader to the substrate with fasteners through the aligned holes. 20.The method of claim 19 wherein fastening comprises riveting the heatspreader to the substrate with rivets.
 21. The method of claim 19wherein the fasteners comprise barbed connectors, and wherein thesubstrate includes standoffs, and wherein fastening comprises pushingthe barbed connectors through the aligned holes into the standoffs. 22.The method of claim 19 wherein the substrate includes standoffs andwherein the barbed connectors are provided in the aligned holes of theheat spreader, and wherein fastening comprises snapping the barbedconnectors into retaining elements in the standoffs.
 23. The method ofclaim 19 further comprising: adhering the fasteners to the substrate,the fasteners comprising gripping pins; and sliding the pins through thealigned holes of the heat spreader, wherein fastening comprises slidinga clip over ends of the pins to hold the heat spreader in position overthe die.
 24. The method of claim 19 wherein a thermal interface materialthermally couples the die to the heat spreader, and wherein the methodfurther comprises after fastening, curing the interface material at anelevated temperature.
 25. A system comprising: an organic circuit board;and one or more packages mounted on the circuit board, at least one ofthe one or more packages comprising a substrate and a heat spreadercoupled to the substrate with a plurality of fasteners.
 26. The systemof claim 25 wherein the heat spreader has recesses on a surface oppositethe substrate to receive heads of the fasteners, and wherein thefasteners are rivets and wherein the substrate has holes therethroughaligned with holes in a perimeter region of the heat spreader, therivets to extend through the aligned holes in the substrate and theperimeter region.
 27. The system of claim 25 wherein at least one of thepackages further comprises a die coupled to a central region of the heatspreader with thermal interface material, the die being mounted on thesubstrate, wherein the fasteners couple a perimeter region of the heatspreader region to the substrate, wherein the perimeter region has athickness less than or approximately equal to a thickness of the centralregion, and wherein the substrate has standoffs to align with portionsof the perimeter region, the standoffs having a height approximately atleast as great as a height of the die plus a thickness of the thermalinterface material, the fasteners to be received through holes in theperimeter region aligned with holes in the standoffs